Yet another Mass Participation question

[SerhanB]

Hello,

I'm working on a model resting on elastic foundation which is also very irregular (tunnel underneath). For modal analysis, I'm converting 2 load cases to mass but I couldn't make mass participation to go beyond 70% in each direction even with 150 modes. 

What can be done in this case? I will be happy if you can check the attached model and share your opinions.

Thanks...

[Artur.Kosakowski]

What about running the modal analysis for part of the model being above the top supports level only? You may set disregard density in its parameters and apply loads (including self weight) you want to convert into masses to the above the ground part of the model only.

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[SerhanB]

Hi Artur,

Thanks for your comment. Since this model is a Mock Up of a larger structure, manually dealing with self weight would be really cumbersome. I thought of a similar approach as decreasing mass of foundation panels/walls to a degree that they shall not contribute to overall mass sum.

Eventually this worked and participation reached to ux:85% uy:95%. However increasing mode count do not effect ratios anymore. 

What is your opinion on this method (lowering mass) and I would like to hear your ideas how to participate more mass from upper levels.

Thanks

[Artur.Kosakowski · Accepted solution]

I'd consider this approach

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[SerhanB]

Hi Artur,

Thanks for the effort, I really appreciate it. Your explanation is pretty clear and informative in many aspects! I see that both approaches reach to similar results and decision and modelling preference is up to the engineer.

Have a nice day!